A head-up display device typically includes a projection unit that produces a light beam intended to be directed towards a combiner in order to project images, in particular operating and driving information of a vehicle, in the form of a virtual image, in the field of view of a user, in particular a pilot or motor vehicle driver.
Designed originally for the display of information to pilots of combat aircraft, head-up display devices are increasingly used today in particular in the motor vehicle sector, more particularly in cars of medium and high range. Head-up display devices are reputed to contribute to road safety as they allow drivers to read the information without their eyes leaving the road in front of them. The virtual image containing the displayed information is moreover projected at a distance of a few meters in front of the driver, which allows him to read the information without modification of the accommodation of his eyes.
Head-up display devices exist which use a part of the windscreen as combiner, i.e. as the optical element which combines the light beam containing the information having to be presented to the user with the light coming from the environment. Other head-up display devices include a combiner independent of the windscreen. Such a combiner comprises a strip having the necessary optical properties to deviate at least a substantial part of the beam coming from the projection unit towards the user, while being sufficiently transparent to allow passage at the same time of a substantial part of the ambient light coming from the environment.
It has proved desirable to be able to protect the optical elements of the head-up display device, for example against dust and other detrimental influences, risking deterioration of the projection quality.
Another problem is the adjustment of the head-up display device to the needs of the driver. In particular, because the angle of view (the angle relative to the nominal direction up to which the image can be viewed with sufficient contrast) of a head-up display device is typically fairly small and the position of the eyes of the user can vary greatly from one user to the other, the head-up display device should be provided with means allowing the user to adjust the direction in which the beam carrying the information to be displayed at the height of his eyes is returned.
U.S. Pat. No. 5,394,203 describes a head-up display device comprising a combiner in the form of a reflective strip mounted tilting and acting as a lid that is closed when the device is not in use. However, given that the strip acts as a lid, one of its sides remains exposed to the detrimental influences.
Application WO 2007/057608 presents a head-up display device with a retractable combiner. The combiner is mounted on a movable support so as to be able to be displaced between a display position, in which the combiner is upright facing the driver, and a storage position, in which the combiner is returned back into the case which protects all of the optical and mechanical components of the head-up display device. The limit of travel of the movable support carrying the combiner can be adjusted to obtain adjustment of the angle of slope of the combiner and thus the angle of slope of the axis going from the eyes of the driver to the virtual image.
However, the head-up display device of application WO 2007/057608 does not allow adjustment of the distance at which the virtual image is displayed. Now the adjustment of the projection distance is very advantageous from the ergonomic point of view, as it allows the position of the virtual image to be suited relative to the mechanical architecture of the vehicle (in particular relative to the dimensions of the bonnet). Moreover, this type of adjustment allows the user to suit the display to his viewing conditions.
Document JP 10 333080 discloses a head-up display device with two deflection mirrors in the optical path between the projector and the combiner. The first of the two mirrors from the projector is mounted rotatable or displaceable in translation to be able to change the vertical position of the virtual image in the field of view of the user.
Document US 2005/0024490 describes a head-up display device, in which the last mirror, i.e. the one that is in the field of view of the user is retractable. In its storage position, the mirror forms the lid of the head-up display device. The rear face of this mirror (i.e. the upper face in the storage position) is provided with a foldable cover. This cover is deployed when the mirror is closed to give an appearance of quality to the device. The mirror can be formed as combiner; in this case, the cover is completely retracted when the mirror is in the display position.
Document U.S. Pat. No. 5,237,455 describes a head-up display device with a retractable combiner. The opening through which the combiner can be manually removed from and returned to the case is closable by a curtain. The opening and closing of this curtain is also performed manually.